This invention relates to an end feed, extrusion apparatus and process.
Center feed, extrusion dies are commonly used in today's plastics industry. A flow stream entering the manifold undergoes flow divergence, as a result of which there occurs a division of the stream into substreams that flow in generally opposite directions to both ends of the manifold. Pressure drop occurs as each substream flows from the centerline of the manifold to its respective manifold end.
Typically, center feed, extrusion dies have a tear drop-shaped, coat hanger-type manifold. To overcome the pressure drop and produce a substantially equal flow volume of a stream across the stream width, this type of prior art apparatus further includes a single stage, flow pressure-compensating, preland channel. Flow divergence and stream flow in this type of prior art apparatus are generally illustrated in FIG. 1.
Also known is a center feed, extrusion apparatus having a two stage, flow pressure-compensating, preland channel. This type of apparatus is exemplified in U.S. Pat. No. 4,372,739 to Vetter et al and U.S. patent application Ser. No. 852,825 in the name of Peter F. Cloeren.
Flow divergence in a center feed, extrusion apparatus has an adverse impact on layer uniformity of a composite stream of diverse materials. In the course of flow divergence, abrupt and sudden changes occur in flow direction, flow velocity and flow stream geometry, particularly near the centerline of the manifold where a resultant loss of energy is amplified and as a consequence, disuniformity of flow energy loss is accentuated. FIGS. 1 and 2 illustrate working energy loss in the area of flow divergence, in a tear drop-shaped, coat-hanger type manifold.
Each flow stream material has its own "hydraulic value", that is, its own rheological characteristics and properties, in particular temperature dependent characteristics and properties such as melt viscosity, elasticity and so forth. Accordingly, when a composite stream of diverse materials or polymers is subjected to flow divergence, each material reacts differently, with resulting disruption of widthwise layer uniformity. To correct the disruption in layer uniformity, the composite stream may be profiled, that is, the shape of individual layers of the composite stream may be mechanically altered upstream of the place of flow divergence.
An advantage of an end feed, extrusion apparatus is that there is no flow divergence, that is, there is no division of a flowstream into substreams that flow in generally opposite directions, and disuniformity in loss of flow energy accompanying change in flow direction is reduced. U.S. Pat. Nos. 3,583,032 to Stafford, 3,908,170 to Riboulet et al, and 4,880,370 to Krumm exemplify prior art, end feed, extrusion apparatus.
However, according to this prior art, divider blades within the manifold, processing adjustments, or a multi-manifold apparatus are necessary to provide for individual layer uniformity. Moreover, this end feed, prior art is unsatisfactory in further significant respects.
The Stafford and Riboulet et al patents illustrate the use of an end feed, extrusion apparatus having a generally pipe-shaped manifold. However, a drawback of this type of apparatus is the lack of a zone that compensates for substantially unequal flow volume across a stream width, prior to the stream reaching the exit orifice. As a result, this type of apparatus is typically limited to the extrusion of low viscosity materials.
FIG. 3 illustrates my concept of stream flow in an end feed apparatus having a generally pipe-shaped or circular manifold 1 in communication with an elongated, slot-like, exit orifice 2 for extrusion of flat films, as taught by Riboulet et al. FIG. 4 depicts the velocity profile of a stream within the manifold of this type of apparatus.
The Krumm patent illustrates the use of an extrusion apparatus including end feed plates having a "half coat-hanger manifold". Advantageously, these end feed plates include a single stage, flow pressure-compensating zone, and accordingly, may be applicable to the extrusion of higher viscosity materials. However, a half coat-hanger manifold, end feed apparatus is detrimentally affected by substantial non-uniform, die body deflection.
Thus, this end feed, prior art is also severely limited either by lacking a flow pressure-compensating zone, or by substantial non-uniform, die body deflection.
Therefore, there is a need for an improved extrusion apparatus that avoids flow divergence and reduces disuniformity in loss of flow energy accompanying change in flow direction. In particular, there is a need for an improved end feed, extrusion apparatus that not only meets these objectives but also does not require divider blades within the manifold, processing adjustments as described by Riboulet et al, or a multi-manifold apparatus for individual layer uniformity. It would be remarkable if such an improved, end feed apparatus would also be capable of compensating for substantially unequal flow volume across a stream width and in addition reducing non-uniform, die body deflection. It would be advantageous if such an apparatus would be able to process a diversity of materials, both low viscosity and high viscosity, without adjustable parts downstream of the manifold such as a choker bar, and with reduced lip gap adjustment, in providing a web of uniform thickness. Such an apparatus would make possible an improved end feed, extrusion process.